Controllable Universal Supply with Reactive Power Management

ABSTRACT

Apparatus and associated methods involve a controllable supply adapted for controlling switch phasing and pulse width to substantially equalize power in adjacent quadrants of a sinusoidal source voltage waveform to regulate reactive power drawn from the source. In an illustrative example, the supply may, in some embodiments, deliver power to a load at a level responsive to a commanded input signal. In some examples, the power supplied to the load may be adjusted according to the command input signal to a selected value within an operating range. In some examples, the operating range may include a portion or all of 0 to 100% of rated load. Various embodiments may be adapted to supply unipolar or bipolar load excitation. In some embodiments, high power factor may be maintained over a substantial range of commanded power to the load. Certain embodiments may enhance supply efficiency by capturing and recycling inductive load energy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit to U.S. application Ser. No. 61/290,253,entitled “Supply for Lighting Systems,” as filed on Dec. 28, 2009 byBabcock, et al., and to U.S. application Ser. No. 61/290,257, entitled“Rectifier Systems,” as filed on Dec. 28, 2009 by Babcock, et al., theentire contents of each of which are fully incorporated by referenceherein.

TECHNICAL FIELD

Various embodiments relate to operating variable control of loadssupplied from AC sources.

BACKGROUND

Many electrically-operated systems and devices have inductance. Someinductive devices, such as DC (direct current) motors, automotiveignition systems, and some electromagnets, can operate when suppliedwith a unidirectional current. Some inductive devices, such astransformers, AC (alternating current) motors, and fluorescent lights,operate when supplied with a bidirectional current.

In general, inductive elements can store energy in a magnetic field.Typically, the magnetic field is supported by an electric currentflowing through the inductive element. Inductance may be a function ofthe characteristics of a magnetic flux path. For example, inductance insome elements may depend on material properties of a core (e.g., air,steel, and ferrite) in the flux path, and/or a flux density saturationlevel.

The amount of energy stored in a magnetic field of an inductive elementcan be a function of the inductance and the current. In general, theamount of energy stored in the magnetic field increases as currentincreases, and decreases as the current decreases. Accordingly, when thecurrent through the inductive element is zero, the stored inductiveenergy is also zero.

One characteristic of an ideal inductor is that a voltage across theinductor is proportional to its inductance and the time rate of changeof current. This concept may be represented by a formula as: V=Ldi/dt.

Under certain conditions, the energy stored in an inductor can generatepotentially uncontrolled large voltages. This effect may be referred toby terms such as reverse electromotive force (REMF), flyback voltage, or“inductive kick.” As an illustrative example, if an inductor is beingsupplied a current through a switch, and that switch is rapidly opened,then the inductor may have a relatively large change of current (largedi) in a relatively short period of time (small dt). As a consequence,the inductor could generate a correspondingly large voltage (large V).

In some applications, the energy stored in an inductor may be capable ofgenerating sufficiently large voltages to damage or destroy, forexample, an unprotected switch. In some systems, stored inductive energymay be dissipated as heat.

SUMMARY

Apparatus and associated methods involve a controllable supply adaptedfor controlling switch phasing and pulse width to substantially equalizepower in adjacent quadrants of a sinusoidal source voltage waveform toregulate reactive power drawn from the source. In an illustrativeexample, the supply may, in some embodiments, deliver power to a load inresponse to a commanded input signal. In some examples, the powersupplied to the load may be adjusted according to the command inputsignal to a selected value within an operating range. In some examples,the operating range may include a portion or all of 0 to 100% of ratedload. Various embodiments may be adapted to supply unipolar or bipolarload excitation. In some embodiments, high power factor may bemaintained over a substantial range of commanded power to the load.Certain embodiments may enhance supply efficiency by capturing andrecycling inductive load energy.

In one exemplary aspect, a method of managing reactive power, the methodincludes rectifying a substantially sinusoidal source voltage waveformfrom a source to a rectified voltage node, providing a switch arrangedto selectively couple the rectified voltage node to a load anddetermining a pulse width value for turning on the switch to deliver adesired average power to the load. The method further includes receivinginformation about relative power drawn from the source during adjacentquadrants of the source voltage waveform, determining a switch turn ondelay time to substantially equalize power between adjacent quadrants ofthe same polarity, and, controlling the switch during at least twosuccessive half cycles of the source voltage waveform according to thedetermined switch turn on delay time.

In various examples, the method may further include controlling areverse electromotive force associated with rapid turn off of theswitch, and capturing inductive energy stored in the load when theswitch disconnects the load from the rectified voltage node. It mayfurther include returning the captured energy to the load on asubsequent half cycle of the source voltage waveform. In some examples,the method may include providing a capacitor at the rectified voltagenode to provide a leading phase shift to the current drawn from thesource. Determining a switch turn on delay time to substantiallyequalize power between adjacent quadrants of the same polarity mayinclude determining a delay time with respect to a periodic referencepoint on the source voltage waveform. The periodic reference point maybe a zero cross point, and may be a point at which the source voltagewaveform is increasing or decreasing. Some implementations furtherinclude receiving a power command input signal. The step of determiningthe pulse width value for turning on the switch to deliver the desiredaverage power to the load may further include determining a pulse widthvalue in accordance with the received power command input signal.Controlling the switch during at least two successive half cycles of thesource voltage waveform according to the determined switch turn on delaytime may further include controlling the switch according to thedetermined pulse width value.

Certain embodiments may provide one or more advantages. For example,some embodiments may provide an efficiency gain when replacing anexisting interface between a load and a utility feed line. For example,various implementations may compensate for more than the added switchloss by any or all of the following: (i) recapture and recycling ofinductive energy stored in the load (e.g., flyback capture process);(ii) reduced filtering insertion loss by elimination of high frequencyfilter components to attenuate high frequency switching systems; (iii)reduced utility rates from management of reactive power consumption; or,(iv) smooth control of load power within a wide control range (e.g.,dimmability for lighting, or adjustable speed for machines) as needed toconserve energy.

Some implementations may achieve high efficiency, high power factor(e.g., above 0.9), and power regulation within a wide control range fora variety of loads. Exemplary loads that may be supplied by variousembodiments include, but are not limited to, single phase inductionmachines (among other machine types), HID lights with power-regulatedballasts, and battery chargers for telecommunication applications, forexample. Some examples may provide a highly controllable, high powerfactor, low loss, electromagnetically quiet, robust, and universalsupply module capable of supplying regulated power to a wide range of ACand DC load types.

The details of various embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbe apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic representation of an exemplary energyprocessing module with a power stage to supply energy from a DC input toa DC inductive load.

FIG. 2 shows a schematic representation of an exemplary power stage tosupply energy from a DC input to a DC inductive load.

FIG. 3 shows plots of exemplary voltage and current waveforms toillustrate operation of the power stages of FIGS. 1-2.

FIG. 4 shows a schematic representation of an exemplary power stage tosupply energy from a DC input to a DC inductive load.

FIG. 5 shows a schematic representation of an exemplary pair of powerstages to supply energy from a DC input to an AC inductive load.

FIG. 6 shows a block diagram representation of an exemplary energyprocessing system that uses the power stages of FIG. 5 to supply energyfrom an AC input to an AC inductive load.

FIG. 7 shows a flowchart of an exemplary process for controlling theenergy processing system of FIG. 6 to draw low reactive power from theAC source over a range of regulated power to the load.

FIG. 8 shows an exemplary controllable universal supply configured tomanage reactive power drawn from an AC utility source.

FIG. 9 shows exemplary loads for (a) a high intensity discharge (HID)lighting application, and (b) induction machine applications, configuredto receive power from the supply of FIG. 8.

FIG. 10 shows an exemplary rectifier load configured to connect toreceive power from the supply of FIG. 8, and to supply power to anindustrial battery charger.

FIG. 11 shows an exemplary set of electrical waveforms illustratingperformance of an experimental HID light load as discussed withreference to FIG. 9( a) when supplied by the supply of FIG. 8 over arange of power levels and using the process of FIG. 7.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EXAMPLES

FIG. 1 shows an exemplary system 100 in which energy may be supplied toinductive and/or resistive loads at a controllable rate with highefficiency and low electromagnetic noise. The system 100 of this exampleincludes an energy processing module 105 that receives energy at aninput, processes the energy, and delivers unidirectional current tosupply energy to a load connected at an output. The module 105 includesa power stage 110 that operates in response to control signals from acontroller 115. In operation, the controller 115 controls the operatingstates of switches in the power stage 110 according to a sequence ofoperating states that may, for example, be repeated in a cyclicalpattern. In an exemplary cycle of operation, the controller 115generates a sequence of operating states that cause the power stage 110to store energy from a power source 120 into an inductive load 125,control a reverse electromotive force (REMF) that may develop when theinductive load 125 is disconnected from the source 120, dischargeinductive energy from the load into a capacitance, and then dischargethe capacitance to store energy back into the load 125 on a subsequentcycle. In various embodiments, the power stage 110 may deliversubstantially unidirectional current flow to the load 125. Someembodiments may completely discharge stored inductive energy from theload 125 during each cycle.

One exemplary cycle of operation of the power stage 110 includes asequence of operating states as indicated by arrows A, B, C, D. Forexample, the processing module 105 may draw current from the powersource 120 during a state B of a cycle, while the power stage 110 mayprovide for unidirectional current flow through the load 125 (e.g., DC(direct current) motor) during states A, B, C, and D of the cycle. Insome applications, additional work may be performed during states A, C,and D when no power is being drawn from the power source 120. Examplesof voltage and current waveforms associated with some embodiments of thepower stage 110 are described in further detail with reference to FIG. 3and FIG. 8.

In the depicted example, the power stage 110 includes a pair of inputswitches 130 a, 130 b, which may be operated, in some embodiments, as adouble-pole single throw switch. Some other embodiments (not shown) maybe configured to operate with only one of the input switches 130 a, 130b. The input switch 130 a connects between an input node 135 and anoutput node 140. The voltages of the nodes 135, 140 may be referred toherein as Vin, Vout, respectively. After the input switches 130 a, 130 bare turned on, an input current (Iin) supplied from the power source 120may flow to the input node 135, and through the input switch 130 a tothe output node 140. An output current (Iout) flows from the output node140, through the load 125, and returns through a return node 145 and theinput switch 130 b to the power source 120. As will be described below,the current Iin from the power source 120 may begin to flow some timeafter the input switches 130 a, 130 b are turned on.

The power stage 110 further includes a transitional circuit 150 whichmay be operated to provide a current flow path for the current Iout soas to control an amplitude of a REMF that may be generated when theinput switches 130 a, 130 b open and rapidly disconnect the outputcurrent Iout from the input current Iin. As such, the transitionalcircuit 150 may substantially protect the input switches 130 a, 130 bfrom exposure to potentially destructive REMF voltages. In the depictedexample, the transitional circuit 150 includes a unidirectional currentelement (e.g., diode) 155 in series connection with a voltage limiterelement 160 and a transitional switch 165. Exemplary embodiments of thetransitional circuit 150 are described in further detail, for example,with reference to FIGS. 2 and 8-9.

The power stage 110 also includes an energy capture circuit 170connected substantially in electrical parallel with the load 125 and thetransitional circuit 150. In the depicted example, the energy capturecircuit 170 includes an energy capture switch 175 in series connectionwith a capacitor 180 and a unidirectional current element (e.g., diode)185. When the energy capture switch 175 is turned on, the output currentIout can flow from the return node 145 to the output node through thecapacitor 180. Accordingly, inductive energy in the load 125 istransferred to stored charge on the capacitor 180. The rate at whichoutput current Iout falls depends substantially on a capacitance valueof the capacitor 180. As one skilled in the art will appreciate,increasing the capacitance value may result in a longer time for theIout to “reset” to zero. In various embodiments, the capacitance valueof the capacitor 180 may be selected or dynamically adjusted to resetthe output current Iout to zero before the next operating cycle. Afterthe output current Iout resets to zero, the unidirectional currentelement 185 substantially prevents Iout current from flowing in theopposite direction. As such, resonances or oscillatory currents may besubstantially prevented with respect the output node 140 of the powerstage 110.

Finally, the depicted power stage 110 includes diodes 190 a, 190 b toreturn captured energy from the capacitor 180 to the input node 135.During steady-state operation, for example, the capacitor 180 suppliesthe captured energy through the diodes 190 a, 190 b and back to the load125 when the input switches 130 a, 130 b are turned on. In this example,a blocking diode 195 substantially prevents the captured energy fromflowing back to the power source 120. This energy recovery mayadvantageously improve efficiency, for example, in applications in whichsubstantial inductive energy can be recovered from the load andre-supplied to the load on a subsequent operating cycle.

In various applications, the controller 115 may generate one or morecontrol signals to control the switches 130 a, 130 b, 165, and 175during an exemplary cycle of operation. To aid understanding of anexemplary operation of the power stage 110, time period indicators A, B,C, D are shown on FIG. 1 to indicate current flows at successive timeperiods within a typical cycle of operation. Exemplary voltage andcurrent waveforms during each of the indicated time periods aredescribed in further detail with reference to FIG. 3.

In the example depicted in FIG. 1, an exemplary cycle of operationbegins with a time period A. At the beginning of the time period A, thecapacitor 180 may be charged with energy captured from a previousoperating cycle. During the time period A, the input switches 130 a, 130b are turned on, and the capacitor 180 may discharge its stored energythrough the diodes 190 a, 190 b, the switches 130 a, 130 b, and the load125. During the time period A, energy that is delivered to the load 125is drawn substantially from the capacitor 180. The time period A mayend, for example, when the capacitor 180 discharges to a point that thediode 195 is no longer reverse biased.

At the beginning of the time period B, the input switches 130 a, 130 bremain turned on, and the power source 120 drives current through thediode 195, the switches 130 a, 130 b, and the load 125. Although variousembodiments have been described with reference to the figures, otherembodiments are possible. For example, this document describes exemplarysystems for new electric machines and related apparatus and methods forsupplying and/or generating electrical excitation using embodiments ofthe new electrical machine systems. Various exemplary systems includeswitching modules. For all purposes, including for example itsdisclosure of exemplary switching modules as described with reference toFIGS. 1-4, this document incorporates by reference the entire contentsof U.S. Pat. No. 7,602,157 to Babcock, et al., entitled “SupplyArchitecture for Inductive Loads.”

Some disclosed embodiments include switch modules in combination withtransformers. For all purposes, including for example its disclosure ofAC operation as described with reference to FIG. 3A, this documentincorporates by reference the entire contents of U.S. Publ. 2009/0073726to Babcock, et al., entitled “Current Waveform Construction to GenerateAC Power with Low Harmonic Distortion from Localized

During the time period B, energy that is delivered to the load 125 isdrawn substantially from the power source 120. The time period B mayend, for example, when the on-time of the input switches 130, 130 bcorresponds to a duty cycle set by the controller 115, or when theoutput current Iout reaches a threshold value. At the end of the timeperiod B, the controller 115 may command the input switches 130 a, 130 bto transition to an off (e.g., non-conducting) state.

Prior to the end of the period B, the controller 115 may generate acommand to turn on the transitional switch 165 to minimize delay inallowing the output current Iout to flow through the transitionalcircuit 150. At the beginning of the time period C, the load generatesthe REMF voltage in response to the opening of the input switches 130 a,130 b. The REMF voltage may forward bias the unidirectional currentelement 155, such that the output current Iout flows substantiallythrough the transition circuit 150. The voltage limiter 160 may operateto substantially control (e.g., limit, clamp, or the like) the REMFvoltage to a value that, for example, is substantially within thevoltage ratings of any devices that could be exposed to the REMFvoltage. During the time period C, some inductive energy may betransferred from the load 125 to the voltage limiter 160. In variousembodiments, the time period C may be sufficiently short in durationthat the amount of energy transferred to the voltage limiter isrelatively small and can be, for example, dissipated as heat (e.g., in aresistor) without significantly reducing overall efficiency. In someembodiments, the controller 115 may generate a signal to turn on theenergy capture switch 175 before or during the time period C. As theenergy capture switch 175 turns on and becomes capable of conducting theoutput current Iout, the time period C may conclude, and the controller115 may generate a signal to turn off the transitional switch 165.

At the beginning of the time period D, the output current Iout flowssubstantially through the energy capture switch 175, the capacitor 180,and the unidirectional current element 185. As such, stored inductiveload energy, which is supported by the output current Iout, getstransferred to the capacitor 180 during the time period D. The timeperiod D may end, for example, after the output current Iout falls tozero. Upon detecting that the output current Iout has reset to zero, orafter allowing a time sufficient to ensure the output current Iout issubstantially reset, the controller 115 may generate a signal to turnoff the energy capture switch 175.

Following the time period D, there may be, in some embodiments, anadditional period of time from the end of the time period D until theend of the operating cycle. In some applications, for example, thevoltage limiter 160 may be discharging a capacitor into a resistor orthrough a switch (not shown) during this additional time period. Invarious applications, a motor may be coasting, for example, during thisperiod.

In various examples, the controller 115 may time the operation of someor all of the switches 130 a, 130 b, 165, and 175 during an exemplaryoperating cycle as follows. The transitional switch 165 may be turned onprior to turning off the input switches 130 a, 130 b. The diode 155 maysubstantially block current flow through the transitional circuit 150until the output current Iout starts to decrease and a REMF voltage isgenerated by the load 125. The transitional circuit 165 may be turned onearly enough to substantially minimize a delay time for the outputcurrent Iout to start flowing through the transitional circuit 150. Theenergy capture switch 175 may be turned on at any one of a number oftimes, which may be before, at the same time, or after the transitionalswitch 165 is turned on. As the energy capture switch 175 starts toconduct a substantial portion of the current Iout, the transitionalswitch 165 may be turned off.

In another embodiment (not shown), the power stage 110 may operatesubstantially without an actively controlled transition circuit, such asthe transition circuit 150. In such embodiments, the energy captureswitch 175 may be turned on while the input switches 130 a, 130 b areconducting the output current Iout. The unidirectional current element185 may be reverse biased until the output current Iout starts todecrease, at which point the REMF voltage may forward bias theunidirectional current element 185 such that the output current Ioutwould start to flow through the energy capture circuit 170. In variousexamples, passive voltage clamping circuitry, examples of which aredescribed with reference to FIGS. 2 and 8-9, could optionally be used tocontrol a REMF voltage amplitude, for example, in the voltage limiter160. In some embodiments, the transitional switch 165 may be turned oncontinuously during normal operation, or replaced with a short circuit,for example. In some embodiments, the transitional switch 165 may beturned on during part or all of the time periods A and/or B, forexample.

When the input switches 130 a, 130 b open, inductance in the load 125may generate a reverse electromotive force (REMF), which, in general,may be considered to represent a voltage with an amplitude thatcorresponds to the time rate of change of the load current (e.g.,dIout/dt). Reducing Iout to zero very rapidly, for example, may generatea substantial REMF voltage in the inductive load 125.

Fast transient voltages associated with a large REMF could generate, forexample, substantial radiated and/or conducted electromagnetic radiation(e.g., radio frequency noise). Generally, systems that generate suchnoise energy may employ shielding and/or filtering, which may reduceefficiency and increase the cost, volume and/or weight of the system.

Moreover, large REMF voltages may impart substantial voltage stress tocomponents, such as switches, diodes, capacitors, and transistors. Insome examples, a single pulse of a large REMF voltage can substantiallydamage or destroy a semiconductor device, for example, by exceeding thedevice's voltage rating.

The power stage 110 provides a capability for rapidly switching currentsupplied to an inductive load. In one aspect, the power stage 110includes a transitional circuit 150 in parallel with the load 125. Insome embodiments, the transitional circuit 150 may provide a path forthe load current Iout to flow so that dIout/dt is controlled during abrief transition period after the input switch 130 opens. Controllingthe dIout/dt for the inductive load 125 may substantially reduce theREMF voltage. At sufficiently small values of REMF voltage, for example,the associated transient energy may be insufficient to excitesubstantial conducted or radiated noise. As such, shielding and/orfiltering may be substantially reduced or eliminated in some systems.

In another aspect, some embodiments of the power stage 110 may includeone or more semiconductor switch elements with high peak reverse voltagecapability. Some embodiments may use high voltage devices to improvereliability in systems that switch inductive loads. In some embodiments,one or more of the switch elements may combine a high peak reversevoltage capability with very short turn-on and/or turn-off times.Examples of various switch elements that may be used in the power stage110 are described in further detail with reference to FIG. 2.

In the depicted example, the controller 115 receives a control input. Invarious examples, the control input may couple the controller 115 to afeedback signal from one or more position, torque, speed, voltage, lightintensity, or current sensors, or a combination of signals from theseand/or other sensors. In some other examples, the control input maycouple the controller 115 to one or more command inputs, which may be inthe form of analog (e.g., potentiometer, relay contacts, and the like)and/or digital (e.g., serial, parallel) input signals.

In response to such feedback and/or command input signals, thecontroller 115 may adjust operation of the power stage 110, for example.In various examples, the responses to control input signals may include,but are not limited to, turning the output on or off, increasing ordecreasing the average output voltage, maintaining the output currentwithin predetermined limits, adjusting operating duty cycle and/orfrequency, for example. In some implementations, such control actionsmay be used to, for example, maintain the output current or loadtemperature within predetermined limits, regulate a motor shaft positionand/or speed, or control a lamp output intensity.

Exemplary embodiments and features of the controller 115 are described,for example, with reference to FIG. 6

In various examples, the energy stored in the load (e.g., reactiveenergy) may be supported by a unidirectional current supplied by thepower stage 110. Unidirectional current loads may include, but are notlimited to, DC motors, inductors (e.g., air core, iron core, laminatedsteel core, high permeability cores), electromagnets, lighting (e.g.,direct current high intensity discharge elements), DC transmissionlines, or combinations of these and/or other unidirectional currentloads. Some embodiments may be used as, or as replacement for,mechanical relays or contactors. For example, the power stage 110 mayact as an electronically controllable switch to a DC load, for example,that may be controlled by a switch, optical signal, magnetic signal, orelectrical signal, which may be generated by, for example, a processor,timer, control circuit, or other element (e.g., bimetallic strip, levelsensor, humidity sensor, or the like).

Some other embodiments may operate to supply energy to unidirectionalcurrent and/or bi-directional current loads that are substantiallyinductive, substantially resistive, or partially resistive and partiallyinductive. Bidirectional current loads may include, but are not limitedto, AC motors (e.g., synchronous, brushless DC, induction), DC motors(e.g., forward and reverse torque), resistors (e.g., heating elements),inductors (e.g., air core, iron core, laminated steel core, highpermeability cores), electromagnets, lighting (e.g., fluorescent, highintensity discharge), AC transmission lines, transformers, orcombinations of these and/or other bi-directional current loads.Examples of energy processing modules that are capable of supplyingunidirectional and/or bidirectional current loads are described infurther detail with reference, for example, to FIGS. 5-7.

FIG. 2 shows a schematic representation of an exemplary power stage tosupply energy from a DC input to a DC inductive load. In the depictedembodiment, the unidirectional current element 185 is implemented withan SCR that may be controlled to conduct current during time period D.

In the depicted example, the switches 130 a, 130 b, 175 are implementedwith a gated unidirectional current element connected in series with acontrolled semiconductor switch. In some embodiments, each switch may becontrolled to provide zero current turn on for the controlledsemiconductor switch (e.g., IGBT) and/or controlled turn-off for thegated unidirectional current element (e.g., SCR). In an illustrativeexample, which is not meant to be limiting, any of the switches 130 a,130 b, 175 may be turned on by supplying an enabling signal to a controlterminal (e.g., gate, base) of the controlled semiconductor switch;after the controlled semiconductor switch has had sufficient time tosubstantially transition to a substantially high conductance state, afast turn-on time gated unidirectional current element may be controlledto turn on. The relative timing of the enabling signal to the controlledsemiconductor switch and to the gated unidirectional current element maydepend, at least in part, on the turn-on transition times of thedevices. In various embodiments, the enabling signals to the controlledsemiconductor switch and to the gated unidirectional current element maybe generated in response to one signal (e.g., substantiallysimultaneous), or the signals may be separated in time by a controlleddelay (e.g., based on hardware or software timers, based on events asdetermined by a processor executing instructions, and/or analog delaycircuit, or the like). In some embodiments, enabling signals from thecontroller 115 may be coupled to one or more of the devices, forexample, via suitable gate supply circuits, some of which may include,but are not limited to, optical, magnetic (e.g., pulse transformer)circuits. In various embodiments, the gated unidirectional currentswitch may include, but is not limited to, an SCR (silicon controlledrectifier), DIAC, TRIAC, flash tube, or the like. In variousembodiments, the semiconductor switch may include one or more seriesand/or parallel combinations of IGBTs (insulated gate bipolartransistors), MOSFETs (metal oxide semiconductor field effecttransistors), BJTs (bipolar junction transistors), Darlington pairs,JFETs (junction field effect transistors), vacuum tubes, or the like.

Typical switching transition times may be, for example, between about 2and about 10 microseconds, although embodiments may be used withsubstantially faster or slower switching times. In an illustrativeexample, the time for the switches 130 a, 130 b to turn completely offand the switch 175 to turn on may typically take about 5 microseconds.In some examples, the transitional switch 165 may conduct current duringat least those 5 microseconds. In some embodiments, the voltage limiter160 may substantially conduct the load current in response to the REMFvoltage in, for example, 10 to 40 nanoseconds.

Also depicted in FIG. 2 is an exemplary embodiment of the voltagelimiter 160, including a parallel resistor and capacitor network. Invarious implementations, the capacitor may be implemented as one or morecapacitors in series and/or parallel combinations. For example,capacitors of with a range of frequency response characteristics may beused to respond to the REMF voltage over a wide frequency range. In someembodiments, which may be used in higher switching frequencyapplications, the voltage limiter 160 may include a controlled switch to“dump” charge stored on a capacitor during the time period C. In thisembodiment, the capacitor 180 is implemented across the input terminalsof the module 110. In other embodiments, the capacitor 180 may beimplemented in whole or in part within the module 180, and may besupplemented with additional external parallel capacitance to suit awide variety of application conditions, for example.

In this embodiment, the transitional switch 165 is depicted as beingimplemented with a semiconductor switch. In various implementations, thetransitional switch 165 may be implemented, for example, with one ormore IGBTs, MOSFETs, BJTs, Darlington pairs, JFETs, vacuum tubes, or thelike. In addition, the power stage 110 of this embodiment includes adiode 210 connected between the transitional switch 165 and the outputnode 140. In some embodiments, the diode 210 may provide additionalprotection for the transitional switch 165, for example. In someexamples, the diode 210 may replace the diode 155.

FIG. 3 shows plots of exemplary voltage and current waveforms toillustrate operation of the power stages of FIGS. 1-2.

In this example, a plot 300 illustrates that the power source 120provides a unipolar input voltage. In this case, the voltage may be thatsupplied by a battery. In other examples, the power source 120 may beany other suitable unipolar or DC source, such as a half- or full-waverectified AC signal, for example. In some applications, the power source120 may exhibit a voltage stiff characteristic, which may be provided,for example, by a substantially large hold-up capacitor. In some otherapplications, the power source may provide a rectified AC signal withouta substantial hold-up capacitance. In such applications, the voltage ofthe unipolar power source 120 may drop to within one or two diode dropsof the AC supply voltage, for example, during the time period B when theoutput current Iout is supplied substantially by the power source 120.

The plot 305 illustrates that the power source 120 supplies the inputcurrent Iin to the load during the time period B (e.g., Iin=Iout), andnot during any other time period of the exemplary operating cycle.

The plot 310 illustrates that Vin at the input node 135 is elevated atthe beginning of the time period A, which reflects the charge on thecapacitor 180. The plot 315 of the output current Iout illustrates thatthe discharge of the capacitor 180 during the time period A suppliesreal energy to the load, which may advantageously reduce the power drawnfrom the power source 120 during the operating cycle.

The plots 310, 315 also show the charging of the capacitor 180 and acontrolled decrease in output current Iout in the time period D. Thecontrolled decrease of Iout may advantageously control an amplitude ofthe REMF.

The plot 320 illustrates, in a magnified view, a portion of the outputcurrent Iout waveform around the time period C in the plot 315. In someexamples, the time period C is short relative to the time periods A, B,and D. During the time period C in this example, the slope (e.g.,dIout/dt) of the plot 315 is controlled substantially by operation ofthe voltage limiter 160. In some embodiments, the slope may becontrolled sufficiently well such that the amplitude and noise energyassociated with the REMF voltage signal may be substantially reduced.

In some applications, successive operating cycles may occur withoutinterruption for an indefinite period during which energy may besupplied to the load. For example, operating cycles may have asubstantially fixed period, which may include, but is not limited to,periods of between about 10 and about 20 milliseconds, or between about1 and about 30 milliseconds, or between about 50 and about 1000microseconds, or less than 60 microseconds, for example. In someapplications, one or more finite number of successive periods may beinterrupted by variable times of not supplying power to a load. In someembodiments, the duration of an operating cycle may be varied accordingto load requirements, an input command, or other requirements (e.g., toavoid an audible resonance frequency, filtering requirements,synchronization to a utility supplied voltage).

FIG. 4 shows a schematic representation of an exemplary power stage 110to supply energy from a DC input to a DC inductive load.

In the depicted embodiment, the power stage 110 has an array of diodes405, each of which is connected from the switch 175 to a capacitor in anarray of parallel-connected capacitors forming a capacitance 410. Invarious implementations, the module or systems may incorporate some orall of the capacitance 410, which may include an array of parallelcapacitors to implement the capacitor 180. In some embodiments, one ormore of the individual capacitors may each have a different frequencyresponse characteristic (e.g., inductance) such that the array ofcapacitors 410 may effectively capture energy from the inductive loadover a wide range of frequency components, for example, in the REMFvoltage signal.

Also depicted in this embodiment is a diode array 405 connected betweenthe energy capture switch 175 and one of the capacitors in the array ofcapacitors 180.

The parallel diodes 405 may, in some embodiments, advantageously reduceringing and/or oscillations among the capacitors in the capacitance 410.The capacitor 410 may be implemented using two or more parallelcapacitances that may provide wider response bandwidth (e.g., lowinductance paths) and/or increased capacitance. Optionally, the array ofdiodes may be implemented as a single diode (e.g., diode 190 b of FIG.1). In some implementations (not shown), a controllable device such asan SCR may optionally be included in the path carrying current duringtime period D, an example of which is described with reference to theelement 185 in the FIG. 2. Such an SCR may advantageously increase peakvoltage withstand capability, and/or reduce undesired (e.g.,inter-electrode, parasitic) capacitance, for example.

FIG. 5 shows a schematic representation of an exemplary pair of powerstages 110 a, 110 b to supply energy from a DC input to an AC inductiveload. In this embodiment, the power stages 110 a, 110 b aresubstantially similar in that they have substantially the same circuitryand draw power from the same power source (e.g., through the diode 195).They differ primarily in the timing of their output signals. In variousembodiments, the power stages 110 a, 110 b may alternately supply outputcurrent to the load. In particular, the power stage 110 a may supplyunidirectional output current A, B, C, D in a first direction to theload, and the power stage 110 b may supply unidirectional output currentA′, B′, C′, D′ in a second direction to the load. In someimplementations, the capacitor 410 may be implemented using two or moreparallel capacitances that may provide wider response bandwidth (e.g.,low inductance paths) and/or increased capacitance, as described inembodiments with reference to FIG. 4, for example.

In an illustrative embodiment, a controller (not shown) may generatecontrol signals to perform an operating cycle using power stage 110 a.During power stage 110 a's operating cycle, the controller may turn offall of the switches in the power stage 110 b, thereby preventing anyoutput current from the stage 110 a from flowing in the stage 110 b.Similarly, the controller may disable the stage 110 a when the powerstage 110 b performs its operating cycle.

FIG. 6 shows a block diagram representation of an exemplary energyprocessing system that can use the power stages of FIG. 5 to supplyenergy from an AC input to an AC inductive load. The system 600 receivesAC power input from an AC power source 605, and supplies an AC poweroutput to operate an AC load 610.

In the depicted example, the energy processing module 105 includes twopower stages 110 a, 110 b, and a controller 615. Using the controller615, the energy processing module 105 may provide automatic andintelligent control to the power stages 110 a, 110 b to improveefficiency and/or control a power factor of the AC power input. Forexample, the energy processing module 105 may control REMF of the loadand capture and re-use inductive load energy to provide high energyefficiency. Additionally, the energy processing module 105 may bedigitally controlled. In some examples, the controller 615 may beprogrammed to control the power stages 110 a, 110 b according to variousinputs (e.g., user inputs, analog inputs, and/or communication networkinput). For example, the controller 615 may also include software andhardware to control the switches in the power stages 110 a, 110 b basedon user input and/or in response to specified events (e.g., AC brownoutconditions, load fault conditions, time of day events, or the like).

The system 600 also includes an input stage 620. The energy processingmodule 105 receives the AC power input from the AC power source 605 viathe input stage 620 and supplies the AC power output to the load. Insome implementations, the AC power source 605 may supply power from anelectrical power distribution network (e.g., utility power at about50-60 Hz, or marine/aviation power at about 400 Hz). The input stage 620may precondition an input voltage, for example, by smoothing and/orrectifying input power for the energy processing module 105.

As shown, the input stage 620 includes a diode bridge rectifier 625 anda capacitor 630 to filter the DC power output. In some implementations,the capacitor 630 may reduce the variation in the DC output voltagewaveform from the bridge. In some examples, the capacitor 630 may betuned for wave shaping to improve power efficiency of the energyprocessing module 105. In various embodiments, the capacitor 630 may besized to effectively provide input current wave shaping thatsubstantially reduces crest factor by reducing current peaks andassociated AC current harmonics.

In some implementations, the capacitor 630 may raise the DC averagevoltage to supply the energy processing module 105. In some examples,the higher DC voltage may be used to start the load 610 and improvevarious types of inductive device performance. In some examples, theincrease in DC voltage levels may also be used to overdrive line lossesto maintain inductive device performance.

Using the energy processing module 105, the AC power source 605 maysupply unidirectional and/or bidirectional current to a load, such asthe load 610. The load 610 may include a single device (e.g., motor) ormultiple devices (e.g., a bank of lights).

In the depicted example, the load 610 includes a transformer 635 thatreceives the bidirectional (e.g., AC) power output from the energyprocessing module 105. In one implementation, the transformer 635 maytransform the AC power output voltage from the energy processing module105 to a load voltage (e.g., 200 V-500 V) that is used by the load 610.For example, the transformer 635 may step-up a low output voltage (e.g.,100 V-220 V) to a higher voltage (e.g., 480 V) for the load 610.

The energy processing module 105 may provide improved power efficiencyand/or control over the input power factor. For example, the energyprocessing module 105 may provide line frequency power factor correctionto improve a power factor drawn from the AC power source 605. In someimplementations, the system 600 may provide line frequency switching(LFS) operations at any in a range of frequencies. In some examples, theLFS process may be timed and synchronized with a phase of the AC powersource 605 to produce, for example, 50 Hz or 60 Hz, switched voltagesand current waveforms for a wide spectrum of inductive loads (e.g., theload 610).

In some examples, the controller 615 may use the LFS process to raisethe electrical efficiency and controllability of standard 50 Hz and 60Hz inductive devices, such as the transformer 635, lamp ballasts, ACinduction motors, DC motors, and power supplies. In some examples, theLFS process may be used in high-power applications and high-powercontrol. For example, very large inductors operating at high powerlevels may be operated with improved stability and energy efficiency. Insome examples, the controller 615 may use the LFS process to providecapabilities that include, but are not limited to, power factor (PF)correction, power level control, high-speed shutdown protection,soft-start and/or hard-start, and universal input (e.g., AC and/or DC).Exemplary applications may include, but are not limited to linefrequency inductive devices such as metal halide and fluorescentlighting, AC induction motors, and welders, for example.

In one example application, a small amount of filter capacitance (e.g.,to provide AC current wave shaping and improved crest factor) may becombined with LFS timing to substantially equalize input power among allfour quadrants. In such an example, the energy processing module 105 maygenerate the AC power output with a high PF.

In some embodiments, the controller 615 may operate to adjust phase andduty cycle to maximize achievable power factor when supplying any outputpower level to the inductive device. For example, a PF of better than0.9 may be accomplished down to about 50% output power levels in someapplications. If a higher PF is required below 50% output power levels,some embodiments may include an AC line reactor at the AC power source605 to raises PF back to acceptable levels.

The controller 615 in the energy processing module 105 may providecertain control functions to adjust PF in the system 600 and to, forexample, reduce REMF, improve energy efficiency, and/or execute softwareinstructions. The controller 615 includes a processor 640 (e.g., a CPU)and a random access memory (RAM) 645 to provide various digital controlfunctions. The controller 615 also includes a non-volatile memory (NVM)645 to store software and data. In the depicted example, the NVM 645stores a code 655. The processor 640 may execute the code 655 to performvarious digital control functions in the energy processing module 105.

In the depicted example, the controller 615 may receives external inputvia a user interface 660, an analog interface 665, and/or acommunication port 670.

From the user interface 660, the controller 615 may receive user input.The user interface 660 may be, for example, a set of dip switches forsetting an operating mode of the energy processing module 105. Forexample, a user may use the user interface 660 to set the output voltageof the energy processing module 105 to be 110 V for operation in theU.S. or 220 V for operation in Europe. In another example, the userinterface 660 may receive user input to dim or brighten intensity of abank of fluorescent lights in a commercial building.

The controller 615 may receive analog input via the analog interface665. The analog input may include signals generated from sensors. Forexample, the system 600 may include a Hall Effect sensor, voltagesensor, current sensor, position sensor, velocity sensor, a temperaturesensor, a light sensor, AC line (e.g., 50-60 Hz) phase sensor, and/orother sensor to detect external environment parameters. In someimplementations, the controller 615 may receive measurement signals froma Hall Effect sensor for proximity switching, positioning, speeddetection, and current sensing applications. In some implementations,the controller 615 may receive measurement of an ambient temperature atfrom a temperature sensor to control power output. For example, theprocessor 640 may adjust to supply maximum output power to an airconditioning load when the ambient temperature is higher than a setpoint. In some implementations, the controller 615 may receivemeasurement of an external light intensity. For example, the processor635 may control the power stages 110 a, 100 b to supply a decreasedpower output to dim the lights (e.g., when the sun is shining, duringoff hours, and the like).

The controller 615 communicates with a communication network 675 via thecommunication port 670. For example, the communication port 670 maytransmit and receive data between the processor 640 and thecommunication network 675. The communication network 675 may include theInternet, a local area network (LAN), and/or a communication cable(e.g., a universal serial bus (USB) cable, a Firewire, other parallel orserial data bus) for communicating with a computer device. Theconnection between the controller 615 and the communication network 675may also be wireless. For example, the communication network 675 may beconnected to the controller 615 using wireless LAN, infrared, Bluetooth,mobile communication network or other wireless network connections.

In some implementations, the controller 615 may receive remote data orinstructions from the communication network 675. In some examples, thecontroller 615 may receive messages that are remotely generated andtransmitted to the controller 615 through the communication port 670.For example, an operator may remotely adjust power output bytransmitting an instruction to the controller 615 from a remote terminalvia a communication network, such as the Internet.

In some implementations, the controller 615 may transmit status and/orother data to the communication network 675. In some examples, there maybe an administrative processor that is connected to the communicationnetwork 675 to monitor operating conditions of the system 600. Forexample, the controller 615 may transmit, via the communication port670, status information indicating the operating conditions of thesystem 600.

In some implementations, the controller 615 may receive software updatesfrom the communication network 675. For example, the code 655 oroperation settings stored in the NVM 650 may be updated by data receivedfrom the communication network 675 via the communication port 670.

The code 655 may include operations that may be performed generally bythe processor 640. The operations may be performed under the control,supervision, and/or monitoring of the controller 615. Operations mayalso be supplemented or augmented by other processing and/or controlelements that may be incorporated by the interfaces 660, 665, 670. Someor all of the operations may be performed by one or more processorsexecuting instructions tangibly embodied in a signal. The processing maybe implemented using analog and/or digital hardware or techniques,either alone or in cooperation with one or more processors executinginstructions.

In some implementations, the processor 640 may execute the code 655 toroute the input power based on conditions at the AC power source 605 andthe load 610. For example, the AC power source 605 may be a wind-powergenerator. When the load 610 is turned off and the wind-power generatoris generating power, the code 650 may include operations to save thegenerated energy in a storage element (e.g., a battery).

In the depicted example, the controller 615 includes a power stagecontroller 680 to control switches in the power stages 110 a, 110 b. Bycontrolling the power stage controller 680, the processor 640 maycontrol the switches in the power stages 110 a, 110 b. The power stagecontroller 680 includes a PWM (pulse width modulator) 685, a switchtiming control 690, and a phase detector 695. In one example, the phasedetector 695 may provide phase information about the input AC source,and the PWM 685 may generate a duty cycle command to determine arequired on time for the input switches that connect the power source tothe load. The switch timing control 690 may use the duty cycle and phaseinformation to generate control signals for the input switches. Thecontrol signals may be timed to draw a current waveform with afundamental frequency substantially in phase with the AC source voltage.The output of the power stage controller 680 may control, for example,at least the fundamental frequency of the output current waveform.

FIG. 7 shows a flowchart of an exemplary process for controlling theenergy processing system of FIG. 6 to draw low reactive power from theAC source over a range of regulated power to the load.

By way of example and not limitation, and as an aid to explanation, thisprocess will be described with reference to the hardware of FIG. 6. Theprocess may be implemented, for example, by the processor 640 in thecontroller 615 performing steps to execute a program of instructions,such as the code 655, which may be stored in a data store (e.g., RAM 645and/or NVM 650).

In the depicted example, a reactive power management process 700 beginsupon initialization at, for example, a predetermined output level (e.g.,default to zero pulse width) for load power, P, at step 705. Referringfor purposes of explanation to FIG. 6, user input may be received at theuser interface 660 to set a desired output level, which corresponds toreceiving a power input command signal, P*, at step 710.

If, at step 715, the power error signal (|P−P*|) is greater than apredetermined threshold, then the controller 615 may, at step 720,adjust the pulse width, PW, of the output signal Vout applied by thepower stages 110 a, 110 b. If, at step 715, the power error signal(|P−P*|) is not greater than a predetermined threshold, then thecontroller 615 may, at step 725, determine if the power factor, PF, isgreater than a predetermined minimum threshold value (e.g., 0.99, 0.98,0.97, 0.96, 0.95, 0.94, 0.93, 0.92, 0.91. 0.90, 0.89, 0.88, 0.87, 0.86,0.85, 0.84, 0.83, 0.82, 0.8, 0.78, 0.76, 0.74, 0.7). If the PF is notgreater than the predetermined minimum threshold value, or afterperforming step 720, then at step 730, the controller 615 calculates apulse start time T1 to equalize power of adjacent quadrants having thesame polarity. In terms of the sinusoidal voltage excitation on the ACpower source 605, quadrant 1 (Q1) and quadrant 2 (Q2) extend from 0 to90 degrees and from 90 to 180 degrees, respectively, are adjacent, andhave positive polarity. Quadrant 3 (Q3) and quadrant 4 (Q4) extend from180 to 270 degrees and from 270 to 360 degrees, respectively, areadjacent, and have negative polarity. T1 may correspond to a phase delaywith respect, for example, to the rising voltage zero crossing of the ACsource 605 at 0 degrees.

If at step 725 the PF is greater than the predetermined minimumthreshold value, then the controller 615 may collect monitoredinformation for at least a predetermined number of one or more cycles todetermine power, P, and PF during a measurement window at step 735.

After performing step 730, the controller 615 calculates at step 740 anupdated switch turn off time, T2=T1+PW, based on the values determinedin steps 720, 730, for example. Then, the controller 615 may interactwith the phase detector 695 and the switch timing control 690 to monitorfor the next full cycle of the AC source (e.g., 0 degrees or 180degrees). At step 745, the EPM 105 waits while no next full cycle isdetected. When the next full cycle is detected, the power stagecontroller 680 may apply operate switches in each of the power stages110 a, 110 b to produce a pulse that starts after delaying T1 from thezero cross T1 before connecting the Vin to the Vout, and turns off T2after the previous zero cross. In some examples, the power stagecontroller 680 may operate the power stages by applying a control pulsesignal at delays of T1, T2 respectively from the rising zero cross (inQ1, Q2) and from the falling zero cross (in Q3, Q4). Examples of T1 andT2 for an experimental HID lamp load over a range of power levels aredescribed in further detail with reference to FIG. 11. In variousexamples, the selection of T1 and T2 may be implemented in an automatedprocess to position the load current drawn from the source to form acomposite input current waveform that exhibits substantially balancedpower between Q1, Q2 and Q3, Q4. The pulse width may be simultaneouslyadjusted to deliver the commanded level of power to the load.

After applying the updated T1, T2 values to control switches at step750, the process performs step 735 as described above. The process 700returns to step 710, and the system may continuously adjust to maintainpower factor while regulating load power in response to the commandsignal, P*, received at step 710.

Although this description refers to power at the load, other relatedparameters may be controlled. For example, where the load 610 includes alighting system, light intensity may be the parameter of interest to theuser who makes input to the user interface 660. Light intensity isrelated as a function of the power delivered to the light by the energyprocessing module 105. In another example, with a motor load, speedand/or torque (or thrust for a linear motor) may be controlled byadjusting the power delivered to the load.

FIG. 8 shows an exemplary controllable universal supply configured tomanage reactive power drawn from an AC utility source. In the depictedexample, a reactive energy management system (REMS) 800 couples to autility power source 805, which may represent a power grid with aregulated sinusoidal voltage at a substantially fixed frequency (e.g.,50, 60, 100, 400 Hz). In some implementations, the REMS 800 may providea substantially grid friendly interface that processes power to presenta high power factor to the utility power source 805 while providinghighly controllable power regulation to any of a number of reactiveloads, including AC or DC type loads.

As depicted, the REMS 800 includes an AC IN Module 810 that couplesdirectly to the utility power source 805, an energy processing module815 that is similar to the Energy Processing Module 105 as describedwith reference to FIG. 6, and a load module 820. The load module 820 maybe any of a number of types of loads, such as motor (AC or DC), battery(e.g., DC), or lamp (AC) loads, examples of which are described infurther detail with reference to FIGS. 9-11.

Power supplied to the load may be adjusted over a range of values, whichmay include part or all of 0 to 100% of rated load power, or a subsetthereof. For examples, HID lamps with self-regulating ballasts may, insome cases, extinguish when the power applied falls below a requiredminimum to maintain an arc. The REMS 800 includes a variable inputcontrol 825 that is depicted as a potentiometer. Other embodiments arepossible, including a fixed set point or a digital PID control system,for example.

The AC IN Module 810 rectifies the AC waveform and supplies inputcurrent to a capacitor 830 to promote phase lead which may help to shapethe input current for reduced reactive power consumption. The power pathcontinues through a blocking diode that isolates the capacitor 830 froma flyback capture capacitor 840. The rectified and/or captured energy iscontrollably pulsed through switches in a pair of opposite polaritypower stages, as has been described. The output power from the EPM 815is applied to the load module 820. Examples of a similar powerprocessing path are also described in further detail with reference toFIG. 6.

A controller 850 may operate the power stage to draw a high power factorand deliver the commanded load power in accordance with the method 700described with reference to FIG. 7, for example. In the depictedexample, the controller 850 receives power and system information from asensor 855 coupled to the AC IN module 810, and from a load sensor 860coupled to the load module 820 and conveyed by signal coupler 865 acrossan isolation barrier 870.

FIG. 9 shows exemplary loads for (a) a high intensity discharge (HID)lighting application, and (b) induction machine applications, configuredto receive power from the supply of FIG. 8.

The REMS 800 of FIG. 8 is capable of operating an HID ballast 900 over awide power range while maintaining high power factor. Experimentalresults of such a lamp are discussed in further detail with reference toFIG. 11.

In the example of FIG. 9( a), the load includes a high impedancetransformer 905, terminals 910 for connection to the EPM 815, an HIDlamp 915, and a power-regulating ballast 920.

The transformer 905 includes primary leakage inductance that can berecaptured during the flyback capture process, as described withreference to FIGS. 1-4, for example. The flyback capture process mayhelp to increase efficiency, provide a mechanism to shape the waveformoutput by the power stages, and the flyback capacitor 840 may generatean extra voltage boost to assist start-up of the arc discharge in thelamp 915.

In the example of FIG. 9( b), the load includes a single phase inductionmotor 950. The motor 950 includes terminals 955 for direct connection tothe EPM 815, split windings 960, rotor cage 965, and capacitor startmodule 970. Here, the REMS 800 is capable of supplying a variable powerlevel to the motor while presenting a high power factor to the utilityfeed 805. Sensors 860 may include a speed or position feedback that maybe controlled by negative feedback adjustment of the pulse width outputby the EPM 815 to the terminals 955. Leakage inductance in the motorwindings may be directly accessed to support the flyback captureprocess.

FIG. 10 shows an exemplary rectifier load configured to connect toreceive power from the supply of FIG. 8, and to supply power to anindustrial battery charger.

In addition to the AC IN module 810 and the EPM 815 of FIG. 8, anexemplary rectifier 1000 depicted in FIG. 10( a) includes a load module1005 that outputs a regulated DC voltage to output terminals 1010. Inparallel across the output terminals 1010 is a capacitor 1015. Therectifier output circuit may optionally include a series low pass filter(not shown). In the load module 1005, a high impedance transformer 1020includes a center tapped secondary winding to permit the depictedrectification.

In operation, the rectifier 1000 may be controlled to position switchingtimes to substantially balance power drawn from the source betweenadjacent quadrants of the same polarity. The output voltage may bemonitored through the isolation barrier to regulate pulse width tomaintain the output voltage at a commanded value.

FIG. 10( b) depicts an exemplary dc-dc converter (e.g., battery charger)1050 that is configured to operate with the EPM 815. In someapplications, the operating frequency may be clock driven at a frequencyselected to be substantially different (e.g., 250 Hz, 400 Hz, 600 Hz),from the line frequency operation (e.g., 60 Hz) of the rectifier 1000.In some examples, the frequency separation may improve control and mayimprove ripple rejection and/or reduce filtering requirements for thecapacitor 1015, for example.

In the dc-dc converter 1050, a load module 1055 includes outputterminals 1060, and a battery 1065 in parallel across the load terminals1060. The load module further includes a low-impedance toroidal coretransformer 1070. The form factor and low stray leakage may beadvantageous in some applications that have low height profilerequirements (e.g., rack mount equipment), or where stray magnetic fluxcould interfere with system operations (e.g., telecommunicationequipment, data centers, etc. . . . ). In order to promote leakageinductance to support the flyback capture for waveform shaping and thusreduced harmonic distortion in the transformer drive signal, the loadmodule 1055 includes a primary side inductor in series with the primarywinding.

FIG. 10( c) depicts a combined system with the subsystems from FIGS. 10(a) and 10(b). The AC utility power supplies the rectifier 1000, whichprovides a line frequency switching rectifier with reactive powermanagement to maintain power factor and flyback capture to maintainefficiency and protect the switches for long mean time between failurefor the semiconductor switches, for example. A DC buss connects theoutput terminals of the rectifier 1000 to the input terminals of thedc-dc converter 1050. The converter 1050 may operate to charge thebattery 1065 with a controlled power pulses, for example, usingsubstantially the same EPM 815 as the rectifier 1000 and switchingcontrol mechanisms described throughout this document.

In some examples, the dc-dc converter 1050 may include a high impedancetransformer in place of the transformer 1070 and inductor 1075. Cost,form factor, and appropriate leakage inductance to support flybackcapture operations may determine appropriate selection of components.

FIG. 11 shows an exemplary set of electrical waveforms illustratingperformance of an experimental HID light load as discussed withreference to FIG. 9( a) when supplied by the supply of FIG. 8 over arange of power levels and using the process of FIG. 7. FIGS. 11 (a-e)exhibit respective (i) power levels of 1100, 900, 800, 700, and 525Watts; (ii) power factors of 0.987, 0.945, 0.931, 0.9, and 0.85; pulsewidths of 82%, 70%, 60%, 45%, and 35%; and, (iv) switch turn on phaseangles of 18, 54, 58, 68, and 72 degrees electrical.

The exemplary waveforms for each of FIGS. 11 (a-e) are arranged from topto bottom as input source voltage (Vac); input current drawn from source(Iin); current into the capacitor 830 (Icap); and current delivered tothe load (Iload). Each waveform plot shows three full cycles capturedfrom an oscilloscope. In the second full cycle on each set of plots, aset of marker lines labeled “1” and “2” are drawn. These marker linesshow the switch turn on time T1 and the switch turn off time T2,respectively, in the quadrants Q1, Q2. In accordance with the controlprocess described with reference to FIG. 7, these plots showexperimental results for modulating the load power to providecontrollable power to the load while adjustments to the phase angle ateach pulse width can maintain reactive power drawn from the load atsubstantially reduced levels.

Although various embodiments, which may be portable, have been describedwith reference to the above figures, other implementations may bedeployed in other power processing applications, such as universal motordrives, DC transmission line stabilization, power factor correction, andnumerous other applications.

Generally, components of a transient voltage limiter may be implementedand arranged to minimize inductance that may increase the response time.

In some embodiments, energy processing modules that are capable ofsupplying bidirectional current loads may also be operated to supplyunidirectional current loads. For example, in the energy processingmodule 500 depicted in FIG. 5, either one of the power stages 505, 510may be operated to supply unidirectional current to the load onsuccessive operating cycles while the other power stage is held in aninactive state. As an illustrative example, if the load includes a DCmotor driving a linear positioning system, then the power stages 505,510 may be activated as needed by a position controller to drive themotor in either advance or reverse directions, respectively, to positionan actuator. Such positioning systems may be used in industrialrobotics, HVAC (heating ventilation air conditioning), and/or numerousother applications.

In some embodiments, the capacitance provided in the energy recoverystage may be adjustable during operation. One or more switches may beprovided, for example, each of which may be individually operated toconnect additional capacitance in parallel and/or in series withcapacitance in the energy capture circuit. Adjustable capacitance may beused to adjust the time required to discharge load current to zerobefore the end of a cycle, for example. Capacitance selection switchesmay be arranged in parallel with a capacitance to short around thecapacitance when turned-on, and/or in series with a capacitance toprevent current flow through the capacitance when the switch is turnedoff. Adjusting fall times of the load current may advantageously providefor adaptation to a wider range of operating conditions, such as loadinductance and/or load current conditions, for example.

In embodiments that include more than one power stage coupled to drive aload, a controller may provide one or more interlock (e.g., AND gate) toprevent control signals from turning on switches in more than one powerstage 110 at a time. In some implementations, an output current fromeach power stage may be monitored, and if a current is detected, allswitches in a corresponding power stage may be disabled.

In various implementations, an energy processing module may be packagedin a module that contains one or more power stages and at least onecontroller. In addition to printed circuit board implementations, someembodiments may be provided in hybrid modules that may containsubcomponents or systems. For example, some implementations may includetwo power stage circuits adapted to provide an AC or two independent DCoutputs, and a suitable controller in a potted module. Some modularimplementations may have a DC input for connection to a unipolar powersource, an AC input for connection to an AC power source (e.g., throughan integrated rectifier module, such as the input stage 620 of FIG. 6),or a combination of one or more such inputs.

Extending the bi-directional output current capability embodimentsdescribed with reference to FIG. 6, for example, additional power stagesmay be configured to supply systems with three or more phases. Forexample, a three phase induction motor with stator windings arranged ina Delta configuration may be supplied by three pairs of power stages,each pair being configured as described with reference to FIGS. 5-6, forexample, and each pair being coupled to supply one phase of the DELTA.Torque, current, speed, phase, position, or other parameters may becontrolled, for example, by a controller supplying control signals tothe controller 615, for example. In some embodiments, encoder, HallEffect, back-emf sensing, or sensorless control, for example, may beused to implement vector oriented control techniques, such as variablefrequency, constant volts per hertz, direct field orientation, orindirect field orientation, for example. In another example, powerstages may be arranged and controlled to supply a three-phase systemWYE-connected transformer, for example. In various multi-phase systems,the input to the power stage may be provided from a DC source and/or anAC source (e.g., single phase, multiple phase with half- or full-waverectification for each phase).

In embodiments with outputs that provide AC (e.g., single phase, threephase, four phase, twelve phase, or the like) may be operated to outputany fundamental frequency to the load, including frequencies up to atleast about 100 kHz or more, such as about 5 Hz, 50 Hz, 60 Hz, 100 Hz,400 Hz, 2 kHz, 5 kHz, 10 kHz, 20 kHz, 60 kHz, 90 kHz, or about 100 kHz.Further, phase of the output fundamental frequency and/or at least oneharmonic frequency may be controlled, for example, to synchronize to autility line voltage signal.

In some implementations with bidirectional or multiple phase capability,two or more power stages may share the same energy recovery capacitance.With reference to FIG. 7, energy captured in the capacitance during thetime period D could be applied to the load in the subsequent time periodA′, and energy captured in the capacitance during the time period D′could be applied to the load in the subsequent time period A.

One or more power processing modules may be coupled to a network thatmay provide for control commands, software updates to be communicated tomodules, and/or to receive status information from modules. Particularmodules may be assigned a network address, such as an IP (internetprotocol) address. For example, each module in an installation may beassigned a unique network address or controlled through a gateway withan IP address.

Although particular features of an architecture have been described,other features may be incorporated to improve performance. For example,caching (e.g., L1, L2, etc. . . . ) techniques may be used. Randomaccess memory may be included, for example, to provide scratch padmemory and or to load executable code or parameter information stored inthe non-volatile memory for use during runtime operations. Otherhardware and software may be provided to perform operations, such asnetwork or other communications using one or more protocols, wireless(e.g., infrared) communications, stored operational energy and powersupplies (e.g., batteries), switching and/or linear power supplycircuits, software maintenance (e.g., self-test, upgrades, etc. . . . ),and the like. One or more communication interfaces may be provided insupport of data storage and related operations.

Some systems may perform electronic processing functions. For example,various implementations may include digital and/or analog circuitry,computer hardware, firmware, software, or combinations thereof.Apparatus can be implemented in a computer program product tangiblyembodied in an information carrier, e.g., in a machine-readable storagedevice or in a propagated signal, for execution by a programmableprocessor; and, methods may be performed by a programmable processorexecuting a program of instructions to perform functions of theinvention by operating on input data and generating an output. Someembodiments can be implemented advantageously in one or more computerprograms that are executable on a programmable system including at leastone programmable processor coupled to receive data and instructionsfrom, and to transmit data and instructions to, a data storage system,at least one input device, and/or at least one output device. A computerprogram is a set of instructions that can be used, directly orindirectly, in a computer to perform a certain activity or bring about acertain result. A computer program can be written in any form ofprogramming language, including compiled or interpreted languages, andit can be deployed in any form, including as a stand-alone program or asa module, component, subroutine, or other unit suitable for use in acomputing environment.

Suitable processors for the execution of a program of instructionsinclude, by way of example, both general and special purposemicroprocessors, which may include a single processor or one of multipleprocessors of any kind of computer. Generally, a processor will receiveinstructions and data from a read-only memory or a random access memoryor both. Elements of a computer may include a processor for executinginstructions and one or more memories for storing instructions and data.Generally, a computer will also include, or be operatively coupled tocommunicate with, one or more mass storage devices for storing datafiles; such devices may include, but are not limited to, magnetic disks,such as internal hard disks and removable disks; magneto-optical disks;and optical disks. Storage devices suitable for tangibly embodyingcomputer program instructions and data include all forms of non-volatilememory, including, by way of example, semiconductor memory devices, suchas EPROM, EEPROM, and flash memory devices; magnetic disks, such asinternal hard disks and removable disks; magneto-optical disks; and,CD-ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, ASICs (application-specificintegrated circuits).

Some implementations may be programmed with the same or similarinformation and/or initialized with substantially identical informationstored in volatile and/or non-volatile memory. For example, one datainterface may be configured to perform auto configuration, autodownload, and/or auto update functions when coupled to an appropriatehost device, such as a desktop computer or a server.

In some implementations, one or more user-interface features may becustom configured to perform specific functions. To provide forinteraction with a user, some implementations may provide for a displaydevice, such as a CRT (cathode ray tube) or LCD (liquid crystal display)monitor for displaying information to the user, a keyboard, and/or apointing device, such as a mouse or a trackball, by which an operatorcan access and/or provide input to the computer.

Various implementations may communicate using suitable communicationmethods, equipment, and techniques. For example, the system maycommunicate with compatible devices (e.g., devices capable oftransferring data to and/or from the system 100) using point-to-pointcommunication in which a message is transported directly from the sourceto the receiver over a dedicated physical link (e.g., fiber optic link,point-to-point wiring, daisy chain). The components of the system mayexchange information by any form or medium of analog or digital datacommunication, including packet-based messages on a communicationnetwork. Examples of communication networks include, e.g., a LAN (localarea network), a WAN (wide area network), MAN (metropolitan areanetwork), wireless and/or optical networks, and the computers andnetworks forming the Internet. Other implementations may transportmessages by broadcasting to all or substantially all devices that arecoupled by a communication network, for example, by usingomni-directional radio frequency (RF) signals. Still otherimplementations may transport messages characterized by highdirectivity, such as RF signals transmitted using directional (i.e.,narrow beam) antennas or infrared signals that may optionally be usedwith focusing optics. Still other implementations are possible usingappropriate interfaces and protocols such as, by way of example and notintended to be limiting, USB 2.0, Firewire, ATA/IDE, RS-232, RS-422,RS-485, 802.11a/b/g, Wi-Fi, Ethernet, TCP/IP, IrDA, FDDI (fiberdistributed data interface), token-ring networks, or multiplexingtechniques based on frequency, time, and/or code division. Someimplementations may optionally incorporate features such as errorchecking and correction (ECC) for data integrity, or security measures,such as encryption (e.g., WEP) and password protection.

In some embodiments, capturing and recycling inductive load energy mayinvolve a process for supplying unidirectional current to a load,controlling a reverse electromotive force (REMF), capturing inductiveenergy from the load, and supplying the captured inductive energy to theload. In an illustrative example, an operating cycle may include asequence of operations. First, inductive energy captured from the loadon a previous cycle may be supplied to the load. Second, energy may besupplied to the load from an external power source. Third, a REMFvoltage may be substantially controlled upon disconnecting the powersource from the load. Fourth, the load current may be brought to zero bycapturing the inductive energy for use on a subsequent cycle. In someembodiments, a single power stage may supply a DC inductive load, or apair of power stages may be operated to supply bidirectional current toan AC load.

Some embodiments may operate to maintain substantially unidirectionalcurrent flow during each operating state, which may substantially reduceand/or eliminate resonances and associated electromagnetic noise. Forexample, various embodiments may generate substantially reduced ornegligible energy that may contribute to conducted and/or radiatedelectromagnetic interference (EMI). Some embodiments may operate from awide range of AC and/or DC voltages and frequencies, and supply eitherunidirectional and/or bidirectional current to inductive and/orresistive loads. Some loads may include capacitors, such as lightingballasts or motor starting circuits, for example. Energy recovery andre-use may provide high efficiency at low noise levels. In some AC inputembodiments, control of phase and duty cycle may provide high inputpower factor and harmonic factor. Some embodiments may provide outputpower controllability, which may yield energy savings in applicationssuch as fluorescent lighting, for example. Furthermore, some DC inputembodiments may provide substantial input line stabilization with lowinput line noise while supplying AC or DC outputs to inductive and/orresistive loads. Various embodiments may be implemented in a wide rangeof form factors and/or integrated modules which may provide reducedmanufacturing cost, increased reliability, and/or simplicity of use in awide variety of stand-alone or system integration applications.

A number of implementations have been described. Nevertheless, it willbe understood that various modification may be made. For example,advantageous results may be achieved if the steps of the disclosedtechniques were performed in a different sequence, or if components ofthe disclosed systems were combined in a different manner, or if thecomponents were supplemented with other components. Accordingly, otherimplementations are within the scope of the following claims.

1. A method of managing reactive power, the method comprising:rectifying a substantially sinusoidal source voltage waveform from asource to a rectified voltage node; providing a switch arranged toselectively couple the rectified voltage node to a load; determining apulse width value for turning on the switch to deliver a desired averagepower to the load; receiving information about relative power drawn fromthe source during adjacent quadrants of the source voltage waveform;determining a switch turn on delay time to substantially equalize powerbetween adjacent quadrants of the same polarity; and, controlling theswitch during at least two successive half cycles of the source voltagewaveform according to the determined switch turn on delay time.
 2. Themethod of claim 1, further comprising controlling a reverseelectromotive force associated with rapid turn off of the switch, andcapturing inductive energy stored in the load when the switchdisconnects the load from the rectified voltage node.
 3. The method ofclaim 1, further comprising returning the captured energy to the load ona subsequent half cycle of the source voltage waveform.
 4. The method ofclaim 1, further comprising providing a capacitor at the rectifiedvoltage node to provide a leading phase shift to the current drawn fromthe source.
 5. The method of claim 1, wherein determining a switch turnon delay time to substantially equalize power between adjacent quadrantsof the same polarity comprises determining a delay time with respect toa periodic reference point on the source voltage waveform.
 6. The methodof claim 5, wherein the periodic reference point comprises a zero crosspoint.
 7. The method of claim 6, wherein the periodic reference pointfurther comprises a point at which the source voltage waveform isincreasing.
 8. The method of claim 6, wherein the periodic referencepoint further comprises a point at which the source voltage waveform isdecreasing.
 9. The method of claim 1, further comprising receiving apower command input signal, wherein the step of determining the pulsewidth value for turning on the switch to deliver the desired averagepower to the load further comprises determining a pulse width value inaccordance with the received power command input signal.
 10. The methodof claim 1, wherein controlling the switch during at least twosuccessive half cycles of the source voltage waveform according to thedetermined switch turn on delay time further comprises controlling theswitch according to the determined pulse width value.